Abstract

A variety of techniques are available for studying past variations of solar wind, solar flares, galactic cosmic rays, and micrometeorites. Lumar rock results which average over the recent past ($\sim $ 10 Ma) indicate no major changes in any of these components. At longer times, recent data suggest secular changes in the $^{15}$N/$^{14}$N ratio in the solar wind, possibly due to enhanced solar flare activity. With the deployment of new techniques, it now appears possible to measure solar wind, solar flare, and micrometeorite records in individual grains removed from different layers of lunar cores. Such grains have been exposed for brief intervals of time (10$^{3}$-10$^{4}$a) for times extending at least 10$^{9}$ a in the past. Lunar and meteoritic breccias are promising candidates for extending the record back still further, perhaps close to the beginning of the solar system.